Poly(aryl ether) resins are a class of resins having a variety of uses in forming wire coatings, wire insulation, and electrical connectors. When sulfonated, these resins can be used to form osmosis and reverse osmosis membranes useful in processes to purify a wide variety of liquids, for example in desalination processes to purify saline solutions such as seawater. A representative poly(aryl ether) resin is a polysulfone having the repeat unit structure: ##STR1## n can range from 2 to 200 but is more typically 50 to 100. The above polysulfone is herein sometimes referred to as PSF.
PSF has been sulfonated by a variety of methods. For example, an early method disclosed in U.S. Pat. No. 3,709,841 to Quentin discloses sulfonation using chlorosulfonic acid: EQU PSF+ClSO.sub.3 H.fwdarw.PSF--SO.sub.3 H+HCl (I)
This method may induce chain cleavage, branching, or cross-linking, however (Johnson et al, J. Polym. Sci., Polym. Chem. Ed., 22, 721, 1984). The reaction is also heterogeneous, which can affect reproductibility and the extent of sulfonation.
Noshay and Robeson (J. Appl. Polym. Sci., 20, 1885, 1976) reported a milder sulfonation process using a complex of SO.sub.3 with triethylphosphate, SO.sub.3.PO(OCH.sub.2 CH.sub.3).sub.3, which may minimize side reactions. This process is cumbersome, however, due to the reactivity and toxicity of SO.sub.3 and the exothermic reaction of SO.sub.3 with triethylphosphate.
The sulfonated polysulfone is often converted to the salt form for use in membranes by reaction with a base such as sodium hydroxide: EQU PSF--SO.sub.3 H+NaOH.fwdarw.PSF--SO.sub.3 Na+H.sub.2 O
Salts of sulfonated polysulfone are disclosed, for example, in U.S. Pat. No. 3,875,096 to Graefe et al. and in Johnson et al. and Noshay et al., supra.
Several articles have appeared which report the sulfonation of various organic compounds using trimethylsilyl chlorosulfonate as a sulfonating agent. See Hofmann et al., Synthesis, Sept., 1979, 699-700; Hofmann et al, Liebigs Ann. Chem., 1982, 282-297; Grignon-Dubois et al., J. Organometal. Chem., 124, 1977, 135-142; Duffaut et al., Bull. Soc, Chim. Fr., 1963, 512-517; Felix et al, Angew. Chem. Int. Ed. Engl., 18, 1979, 402-403; and Felix et al, Angew. Chem. Int. Ed. Engl., 16, 1977, 488-489. None of these articles discloses the sulfonation of any polymer, however. Nor do any of these articles suggest using a combination of a silyl halide and a halosulfonic acid in any sulfonation procedure.